Conventionally, an electro-acoustic transducer apparatus having a chargeable secondary battery built in is known. Patent Document, Japanese Unexamined Patent Publication No. 2009-267582, discloses a hearing aid having a non-contact charge function.
In the conventional hearing aid, it has been presumed that two hearing aids are charged in a state where they are disposed in parallel within an area in which a magnetic flux generated by a power transmission coil for supplying electric power can be received. When charging two hearing aids disposed in parallel, a power reception coil inside each hearing aid is deviated from a position of the center axis of the power transmission coil. In this case, there was a problem that charging efficiency is poor because the magnetic flux that passes through the power reception coils is scarce.